Unit 7 Study Guide: Evolutionary History and Speciation

Phylogeny

The evolutionary history of a species or group of related species.

Phylogenetic tree

A diagram that represents hypotheses about evolutionary relationships.

Node (Branch Point)

Represents the most recent common ancestor of all lineages derived from it.

Root

The common ancestor of all species included in the diagram.

Sister Taxa

Groups of organisms that share an immediate common ancestor.

Outgroup

A lineage that diverges early in the history of a group used as a reference point.

Clade

A group of species that includes an ancestral species and all its descendants.

Principle of Parsimony

The simplest explanation requiring the fewest evolutionary events is most likely correct.

Morphological Homologies

Similarities resulting from common ancestry.

Analogous structures

Structures caused by convergent evolution.

Molecular Data

DNA sequences and amino acid sequences used for phylogenetic analysis.

Molecular Clocks

Some genes mutate at a relatively constant rate allowing estimates of evolutionary time.

Speciation

The process by which one species splits into two or more species.

Biological Species Concept

A species is a group with the potential to interbreed and produce viable, fertile offspring.

Reproductive Isolation

The stopping of gene flow between two populations, making them independent evolutionary units.

Prezygotic barriers

Barriers that prevent fertilization.

Postzygotic barriers

Barriers that occur after fertilization.

Allopatric Speciation

Speciation that occurs when gene flow is interrupted by geographic barriers.

Sympatric Speciation

Speciation occurring in geographically overlapping populations.

Gradualism

Evolution proceeds slowly and at a constant rate over long periods.

Punctuated Equilibrium

Species exhibit long periods of stasis punctuated by sudden, rapid change.

Background Extinction

The standard rate of extinction before humans became primary contributors.

Mass Extinction

A rapid decrease in biodiversity on Earth typically caused by catastrophic environmental changes.

Adaptive Radiation

Periods of evolutionary change in which organisms form many new species to fill different ecological roles.

Human Impact

Current human activities driving the potential 'Sixth Mass Extinction.'

Low genetic diversity

Species with low variability at the genetic level, at higher risk of extinction.